China’s unprecedented growth in recent years has come at a terrible price. Two-thirds of its rivers and lakes are too polluted for industrial use, let alone agriculture or drinking. Just 1 in 100 of China’s nearly 600 million city dwellers breathes air that would be considered safe in Europe. At a time when arable land is in short supply, poisoned floodwaters have ruined many productive fields. And last year, ahead of most forecasts, China passed the U.S. to become the world’s largest source of greenhouse gases.

The immensity of these troubles has produced a result that may surprise many outside China: The nation has emerged as an incubator for clean technology, vaulting to the forefront in several categories. Among all countries, China is now the largest producer of photovoltaic solar panels, thanks to such homegrown manufacturers as Suntech Power (STP). The country is the world’s second-largest market for wind turbines, gaining rapidly on the U.S. In carmaking, China’s BYD Auto has leapfrogged global giants, launching the first mass-produced hybrid that plugs into an electrical outlet. “China is a very fast follower,” said Alex Westlake, a director of investment group ClearWorld Now, at a recent conference in Beijing.

Understanding they are in a global race, China’s leaders are supporting green businesses with policies and incentives. Beijing recently hiked China’s auto mileage standards to a level the U.S. is not expected to reach until 2020. Beijing also says it will boost the country’s share of electricity created from renewable sources to 23% by 2020, from 16% today, on par with similar targets in Europe. The U.S. has no such national goal.

While most environmentalists applaud these developments, China watchers are voicing two very different sets of concerns. Some question whether China will really stand by its ambitious targets and are worried by signs of backsliding as the recession in China’s key export markets drags down economic growth. Another group, interested mainly in America’s own industrial future, fears that China’s growing dominance in certain green technologies will harm budding cleantech industries in the U.S. After all, China’s emergence comes just as the Obama Administration is trying to nurture these same types of ventures, hoping to generate millions of green jobs. Many of these U.S. businesses will have trouble holding their own against low-price competitors from China.

Beijing’s green intentions will soon be put to the test. China is in the midst of the biggest building boom in history. A McKinsey & Co. study estimates that over 350 million people—more than the U.S. population—will migrate from the countryside into cities by 2025. Five million buildings will be added, including 50,000 skyscrapers—equal to 10 New York Cities. And as quickly as new offices and houses multiply, they are filled with energy-hungry computers, TVs, air conditioners, and the like, sharply increasing demand for electricity, which comes mainly from coal-powered plants.

There are two real questions here. The first is whether China can invest in new technologies and create a clean energy industry. On that front there should be no doubt, and other countries, like the United States, who want to develop green jobs need to move swiftly in order to compete with China.

The second question, and one that affects global warming, relates to whether China can make real progress on reducing pollution within its own borders. On that question the jury is still out.